1. Field of the Invention
The present invention relates to a laser beam processing machine that emits a laser beam along a liquid column jetted from a jet nozzle to perform laser processing on a workpiece.
2. Description of the Related Art
In the production process of a semiconductor device, a plurality of areas are sectioned by predetermined dividing lines called streets which are arranged in a lattice pattern on the front surface of a substantially disk-like semiconductor wafer, and a device such as IC or LSI is formed in each of the sectioned areas. Individual semiconductor devices are manufactured by cutting the semiconductor wafer along the streets to divide it into the areas in which the devices are formed.
The following method has recently been proposed as a method of dividing a plate-like workpiece such as a semiconductor wafer or the like. A pulse laser beam is directed along streets formed on a workpiece to form laser-processed grooves. Then, the workpiece is fractured along the laser-processed grooves by a mechanical breaking device. (See e.g. Japanese Patent Laid-Open No. Hei 10-305421.)
The laser beam processing machine is used to direct a laser beam along the streets of the semiconductor wafer for formation of the laser-processed grooves. In such a case, the irradiation of the semiconductor wafer with a laser beam causes debris, which adheres to the front surface of the device. This poses a problem of degrading the quality of the device. To eliminate such a problem, when the laser-processed grooves are to be formed along the streets of the semiconductor wafer, the front surface of the semiconductor wafer is coated with a protective coating film and a laser beam is directed to the semiconductor wafer via the protective coating film. However, since the step of applying the protective coating film on the front surface of the semiconductor wafer has to be added, productivity is poor. In addition, since the irradiation of the semiconductor with a laser beam heats the device, there arises a problem of degrading the quality of the device.
The following method is proposed as a laser beam processing method that eliminates the influence of debris caused by the irradiation of a laser beam and also prevents the heating of a workpiece such as a wafer or the like. A string-like liquid column is jetted from a jet nozzle and a laser beam is directed along the liquid column. This laser beam processing method leads the collected laser beam to the workpiece via the string-like liquid column. Therefore, this method has a merit capable of laser beam processing regardless of the focal position of the collecting lens and an advantage in which the degradation of the quality of a workpiece such as a wafer or the like due to heat can be prevented because heat occurring during laser beam processing is cooled. (See e.g. Japanese Patent Laid-Open No. 2006-255769.)